Integrated networks transmit voice, video and data to subscribers via network signal carriers in the form of coaxial cable or optical fiber. An example of an integrated network is a passive optical network (PON), which can deliver voice, video and other data among multiple network nodes, often referred to as optical network terminations (ONTs), using a common optical fiber link. Passive optical splitters and combiners enable multiple ONTs to share the same optical fiber link. An optical line terminations (OLT) transmits information downstream to the ONTs, and receives information transmitted upstream from the ONTs. Each ONT terminates the optical fiber link for a residential or business subscriber, and is sometimes referred to as a subscriber premises node.
An ONT in a PON functions as an active network interface device (NID). An active NID converts information received on a network signal carrier into services suitable for use by various subscriber devices, such as telephone, video and data services. For example, an active NID in a PON converts optical signals received from the network on an optical fiber to electrical signals for transmission to a subscriber device. In addition, the active NID converts information received from the subscriber devices into integrated data for transmission over a network signal carrier, such as an optical fiber.
Some active NIDs have an enclosure with three different covers that serve to protect electronic circuitry and network terminals from environmental conditions and security threats. For example, the electronic circuitry in a NID is typically fabricated on a circuit card and enclosed in a first, inner protective cover to reduce electromagnetic interference (EMI) emissions and susceptibility to EMI. Shielding the circuit card from EMI improves the reliability of the electronic circuitry to convert the data into useful services for the subscriber.
A second, intermediate protective cover encloses both the circuit card and the first protective cover, as well as the connections to the integrated network, and is accessible only by a service technician via a security latch. In this manner, the NID and its protective cover create a demarcation point between integrated network terminals accessible only by the service technician, and subscriber network terminals accessible by the subscriber. The intermediate cover typically encloses network terminals which require training to handle, such as power inputs, safety ground, and the main signal input, which may be carried by coaxial cable, or fiber optic cable, so as to provide safety measures and prevent tampering by the subscriber or others.
The intermediate cover does not cover the subscriber connections. Instead, the subscriber is permitted to access subscriber terminals such as binding posts or jacks for plain old telephone service (POTS) wires, coaxial cables, and data connections in order to disconnect wiring leading into the subscriber's premise and test the outside line directly. For example, the subscriber can test outside phone lines by plugging a modular phone directly into a POTS connection, such as an RJ-11 phone jack in order to determine if there is a problem with the subscriber's wiring inside the subscriber premises or with the network. The subscriber also may have access to lightning protection for telephony, cable television, Ethernet and safety grounding. A third, outer cover encloses the circuit card, the inner cover, the intermediate cover, the network terminals, and the subscriber terminals, providing the NID with protection from moisture, debris, solar loading, animals and other adverse environmental conditions.